1. Field of the Invention
The present invention relates, generally, to an automotive windshield wiper assembly and, more specifically, to a windshield wiper drive mechanism having a gear ratio which varies sinusoidally to produce an advantageous combination of wiper blade drive torque and speed.
2. Description of the Related Art
Windshield wiper systems commonly employed in the related art include pivotally mounted wiper blades which are oscillated across the automotive windshield between an in-wipe position, typically located near the cowl of the vehicle, and an out-wipe position, usually associated with an A-pillar on the vehicle in the case of the driver's side wiper blade. It is typically desirable to maximize the angular velocity of the blade assemblies between the in-wipe and out-wipe positions where the blade assembly is moving across the windshield in front of the driver to reduce the duration of each wipe cycle. On the other hand, it is also desirable to limit noise and inertia loading by reducing the velocity of the blade assemblies as they approach the wipe limits. These are two competing objectives which must be balanced in order to be successfully and economically obtained.
To achieve these objectives, windshield wiper systems in the related art have employed mechanical linkages between the blade assemblies and a drive motor which are designed to produce the designated torque and blade speed but at the expense of economy and efficient use of vehicle space. Special transmissions have also been interposed between the drive motor and blade assemblies for the same purpose. These transmissions can have gear ratios which vary sinusoidally so as to achieve maximum blade velocity between the wipe limits and maximum torque at the wipe limits. More recently, electrical controls have been proposed to achieve these results by varying the output of a variable speed electric motor which powers the windshield wiper systems. However, complex gearing and electronic speed control systems also increase the cost and weight of conventional windshield wiper systems.
Driver visibility has long been an important criteria in automotive design and has led to an increase in windshield surface area over the years. Windshield wiper systems, including drive motors, linkage mechanisms and blade assemblies, have also become larger in order to adequately service the increased surface area of the windshield. However, and as noted above, the oscillating motion of the wiper blade assembly and associated drive hardware causes high accelerations and inertia induced loads in the driving mechanism. Thus, system inertia continues to be a problem in the related art. High system inertia results in wiper pattern growth beyond design limits, including unacceptable contact by the wiper blades with vehicle A-pillars and cowls.
Thus, there continues to be a need in the art for a windshield wiper system capable of maximizing blade assembly velocity between the wipe limits while maximizing torque during wiper blade reversal at the wipe limits. In addition, there continues to be a need for such a windshield wiper assembly which incorporates low system inertia and economical manufacturing costs.